But while this is broadly true, hibernation is far more complicated and mysterious than that. Most of us assume that animals go to sleep in autumn and wake up again in spring, when the weather warms up. Do animals sleep for the whole of hibernation? Some cold-blooded animals, such as wood frogs, produce natural antifreezes to survive being frozen solid. Breathing slows and, in bats, the heart rate can fall from 400 to 11 beats per minute.
How does hibernation work?Ī hibernating animal’s metabolism slows and its temperature plunges – in ground squirrels it can fall to -2☌. How’s this for a hibernation? In 2012-13, during a year of failure of their favourite food, beech mast, five fat (edible) dormice from the Vienna Woods hibernated continuously for 11 months, with one adult female inactive for 346 days! That’s not sleeping away the winter, that’s sleeping away your life. Again, however, this is an example of torpor. Their metabolism slows right down, their breath hardly detectable. Many normally hyperactive hummingbirds do something similar, entering a state of suspended animation. But this is semi-torpor, not hibernation. During cold or wet weather, parent swifts find it hard to catch enough airborne insects, so their chicks back at the nest chill themselves, reducing their metabolism to go without food for 48 hours – enough to survive until the front passes. There’s a world of difference between a deep sleep and hibernation proper. In most winters, the arrangement is perfect, but fatal if the pond freezes solid. They can breathe simply by the exchange of gases through their skin, rather than the lungs, and since they are inactive, they burn very little internal fuel. The big exception among herptiles is the common frog, the adult males of which often winter in the mud at the bottom of ponds. All of these exothermic vertebrates can be roused by warm winter days – frogs may hunt for food and snakes bask in the weak sunshine. On occasion, toads, newts, lizards and even snakes will all gravitate to the same hollow, former enemies entering into a sleepy truce. Natterjack toads bury into the sand, while all British snakes select sites such as disused rabbit burrows for communal quarters known as hibernacula.
The very rare natterjack toad is now found in just a handful of locations in England. The latter are particularly favoured by slow-worms, often in groups, while other lizards hibernate alone in small hollows. All retreat to secluded spots on land, away from direct exposure to the elements – under logs or piles of stones, inside a hole in the ground or in a compost heap, for example. In the UK, frogs, toads and newts all change their behaviour as soon as the frosts start, in October. It might run out of its fat reserves and die before the spring. A short arousal from torpor won’t necessarily harm a butterfly directly, but the costs in energy expended in flying about and looking for a new hibernation site might cause it stress later on. However, there can be a shadow to sunny winter-day forays. The next drop in temperature may send them back into cover again to resume their dormancy. Once again, this is neither unusual nor necessarily fatal. You might also find butterflies on the move inside a house, where unseasonably warm central heating has roused them from a hiding place.
Every year, peacock butterflies, for example, are spotted around Christmas and New Year flying in gardens, with newspapers subsequently predicting the end of the world.Ī peacock butterfly perched on a stone wall in Wiltshire, UK. In the case of butterflies, overwintering teeters between simple torpor and diapause though the insect is outwardly an adult, it may not yet be reproductively mature.Īll these adult insects are liable to be roused by unseasonably sunny days. Of our butterflies, 9 overwinter as an egg, 32 as a caterpillar, 11 as a pupa and 6 as an adult, including the brimstone, red admiral, small tortoiseshell, comma and peacock (plus the very rare Camberwell beauty.) Some insects, such as butterflies, ladybirds and some bees, overwinter in the adult stage. Do butterflies and other insects hibernate? Between November and February, it spends most of its time underground, puts on weight and its body temperature may drop. © Laurie Campbell/GettyĪt the other end of the scale, the badger enters into a state known as winter lethargy.